PhD Scientific Days 2023

Molecular Sciences - Posters B

Analysis of Epithelial-Mesenchymal Interactions in Initial Formation of the Avian Primary Lymphoid Organs

Text of the abstract

Introduction: Primary lymphoid organ development in birds relies on epithelial-mesenchymal interactions and the inductive capacities of immigrating hematopoietic cells. The bursa of Fabricius (BF) is an avian specific, gut associated primary lymphoid organ, which exclusively supports development of B lymphocytes. The epithelial anlage of the BF appears as an ectodermal derived epithelial bud emerging as a diverticulum of the cloaca surrounded by undifferentiated tail bud mesenchyme. In contrast, the thymic stromal environment develops from the endoderm of the third pharyngeal pouch, surrounded by a specialized neural-crest derived pharyngeal mesenchyme, wherein blood-borne lymphoid progenitors are induced to develop into functionally competent T cells.
Aims: The goal of this project is to characterize the role of epithelial-mesenchymal interactions during primary lymphoid organ development.
Methods: We implemented epithelial-mesenchymal tissue recombination combined with in ovo organ culture technique to assess the inductive capacities of embryonic tissues.
Results: Using the chick-quail chimera system, BF rudiment isolated from
9 day old embryo and third pharyngeal pouch dissected from quail embryos at embryonic day 3 were grafted into the coelom of the chick embryo and allowed to develop in ovo for further 14 days. In transplanted quail BF chick hematopoietic cells enter the quail epithelium and induce functional bursal follicles filled with B cells. In pharyngeal pouch grafts thymus developed with reticulo-epithelial cells belonging to the quail, while T cells were derived from the chick host. Next, pharyngeal pouch endoderm was enzymatically isolated and in vitro associated with chicken BF mesenchyme for 24 hours, then cultured in ovo for 14 days. These tissue recombinants were able to develop thymus like morphology, that contained both cortical and medullary regions of quail derived reticular epithelium, colonized by CD8+ T-cells of host origin. In contrast, BF epithelia that are cultured with intestinal mesenchyme never formed follicles and do not contain B cells.
Conclusion: These tissue recombination experiments indicate that the third pharyngeal pouch endoderm can induce thymus differentiation in heterospecific mesenchyme of BF origin. Whether the BF epithelium has the potential for lymphoid follicle formation when cultured with pharyngeal mesenchyme deserves further analysis.

Funding:
SE250+ PhD Excellence Programme
OTKA grant K-138664